It is known practice to use dye compositions containing oxidation dye precursors, which are generally known as oxidation bases, direct dyes or combinations thereof to dye keratinous fibers, more preferably human keratinous fibers, such as hair. Oxidation bases are colorless or weakly colored precursors, which, when combined with oxidizing products, can give rise to colored compounds and dyes via a process of oxidative condensation. The shades obtained with these oxidation bases may be varied by combining them with couplers or coloration modifiers. Direct dyes are, themselves, colored molecules and dyes with affinity for fibers. When direct dyes are applied in the presence of an oxidizing agent, this is referred to as lightening dyeing.
Usually, dye compositions comprise at least one sequestering agent chosen from ethylenediaminetetraacetic acid (EDTA) and derivatives thereof, for instance diethylenetriaminepentaacetic acid (DPTA). The role of these agents is to complex the metal cations liable to be present in trace amounts in the compositions, and also those that may be present on the hair and originating from the ambient air, from the water with which the hair has been washed, or from shampoos or other hair products with which the hair has been treated. Specifically, it is very important to neutralize these metal cations, since they are liable to catalyze oxidation reactions on the hair fibers, in an uncontrolled manner, which may be reflected by severe adverse effects such as embrittlement of the hair or burning of the scalp.
Dye compositions comprising such sequestering agents give good coloration properties, but may, however, be further improved.